1. Field of the Invention
The present invention relates to a method of manufacturing a substrate, and more particularly, to a method of manufacturing a Group III-V compound semiconductor substrate.
2. Description of the Related Art
A semiconductor device is an electronic component in which electronic devices such as a power device, a light emitting device and a light receiving device are implemented on a predetermined substrate using a semiconductor process technology. For example, the power device has a transistor, a metal-oxide-semiconductor field-effect transistor (MOSFET), an insulated gate bipolar transistor (IGBT) and a schottky diode implemented on a substrate, and the light receiving device has a solar cell and a photo sensor implemented on a substrate. Particularly, a semiconductor light emitting device using a GaN-based compound semiconductor can emit blue light, thereby realizing full colors together with existing green and red light emitting devices using GaAs- and InP-based compound semiconductors. Thus, the semiconductor light emitting device using the GaN-based compound semiconductor has come into the spotlight as a light source of various displays.
However, a high-quality GaN single crystal substrate having the same lattice constant and thermal expansion coefficient is required in order to grow a high-quality GaN thin film. Since GaN has a melting point of approximately 2400° C., and partial pressure of Group V nitrogen is much greater than that of Group III elements, nitrogen requires a pressure of approximately 40,000 atm so as to grow a single crystal substrate. It is difficult to grow the GaN single crystal using the current technique of growing a semiconductor single crystal such as Si, GaAs, or InP.
Thus, a heterogeneous substrate such as sapphire (Al2O3) having a large mismatch with GaN in lattice constant and thermal expansion coefficient is currently used, and a heteroepitaxy in which a GaN epitaxial layer is grown using a buffer layer such as AlN or GaN is used to reduce the mismatch.
Various methods are proposed to grow the high-quality GaN single crystal and may be classified into two methods: a method of growing a GaN layer on a heterogeneous substrate and separating the GaN substrate from the heterogeneous substrate using laser lift-off, wet etching, or the like, and a method of growing a GaN layer on a heterogeneous substrate and then cooling them to automatically separate the GaN substrate and the heterogeneous substrate from each other.
As examples of the first method, U.S. Pat. No. 6,440,823 has disclosed a method of growing a GaN layer with low defect on a sapphire substrate using a hybrid vapor phase epitaxy (HVPE) growth method and then separating the sapphire substrate using laser lift-off, and U.S. Pat. No. 6,693,201 has disclosed a method of growing a GaN layer on a GaAs substrate and removing the GaAs substrate using the wet etching.
As examples of the second method, U.S. Pat. No. 6,924,159 has disclosed an automatic separation method in which a thin GaN layer is grown on a heterogeneous substrate, a thin Ti layer is then grown on the GaN layer, a void is formed in the thin GaN layer under the Ti layer by heat treatment under a hydrogen atmosphere, and a thick GaN layer is formed on the thin GaN layer so that a GaN substrate is automatically separated from the heterogeneous substrate by cooling. Also, U.S. Patent Publication No. 2009/0278136 has disclosed a method in which H+ ions are injected into an ELO GaN template on a heterogeneous substrate using metal oxide chemical vapor deposition (MOCVD), a weak layer is formed at a low temperature, a high-quality thick GaN layer is grown at a high temperature, and then the weak layer is automatically separated by cooling.
However, the related art automatic separation method described above has a low yield and high manufacturing cost.